Re: [PATCH v7 6/6] memory: Introduce address_space_to_flatview_rcu()

[Chuang Xu]

Hi, Peter,

On 2023/3/10 下午11:08, Peter Xu wrote:
> On Fri, Mar 10, 2023 at 10:24:25AM +0800, Chuang Xu wrote:
> > In last patch, we wrap vm_load with begin/commit, here we introduce
> > address_space_to_flatview_rcu() to avoid unnecessary enforce commit
> > during vm_load.
> >
> > Signed-off-by: Chuang Xu <xuchuangxclwt@bytedance.com>
> > ---
> >   include/exec/memory-internal.h |  2 +-
> >   include/exec/memory.h          | 20 ++++++++++++++++++++
> >   softmmu/memory.c               |  2 +-
> >   3 files changed, 22 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/exec/memory-internal.h b/include/exec/memory-internal.h
> > index 100c1237ac..1432240449 100644
> > --- a/include/exec/memory-internal.h
> > +++ b/include/exec/memory-internal.h
> > @@ -30,7 +30,7 @@ static inline AddressSpaceDispatch 
> > *flatview_to_dispatch(FlatView *fv)
> >   
> >   static inline AddressSpaceDispatch *address_space_to_dispatch(AddressSpace *as)
> >   {
> > -    return flatview_to_dispatch(address_space_to_flatview(as));
> > +    return flatview_to_dispatch(address_space_to_flatview_rcu(as));
> >   }
> I'm not sure whether this one is always safe.

Previously I considered that there was no address_space_translate_iommu()
traced during vm_load, so I took it as safe. But my trace may not be
able to obtain all cases of triggering do_commit() during vm_load..

> tcg_commit() seems to be safe, but maybe address_space_translate_iommu() is
> not?  Maybe easier to leave this untouched?

Yes, I'll fix it in v8 later.

> >   
> >   FlatView *address_space_get_flatview(AddressSpace *as);
> > diff --git a/include/exec/memory.h b/include/exec/memory.h
> > index d6fd89db64..235e3017bc 100644
> > --- a/include/exec/memory.h
> > +++ b/include/exec/memory.h
> > @@ -1100,6 +1100,9 @@ bool memory_region_transaction_in_progress(void);
> >   
> >   void memory_region_transaction_do_commit(void);
> >   
> > +/*
> > + * We recommend using this by default.
> > + */
> I think this comment doesn't really help.. drop it?
>
> >   static inline FlatView *address_space_to_flatview(AddressSpace *as)

Thanks!